Rough Idle/what is the fuel pressure - 07 C30 T5 auto

[scot850]

This car is becoming a real pain. After cleaning the CEM and main fuse box for corrosion, put it all back, repaired damaged wires to the exhaust cvvt solenoid and TCV. Also replaced the battery, and cleaned the ECM connectors and pins.

After rebuilding, checked the alternator (concerned it may have been damaged by a mechanic leaving the main ground disconnected and over heated the battery). The reading unloaded was 14.6V.

Started the car and it went to a high idle around 1300 rpm and then dropped to 900 ish rpm. Thought I could feel a slight misfire.

Took the car for a gentle warm up around our neighborhood, and the onto a larger road once it was warmed up. Car pulled hard and no codes.

Drove back home and as I was backing into the garage, the idle dropped and the car started running a little rough. Idle is around 800 rpm.

Left the car in the garage to fix itself.

Today went out and connected a fuel pressure gauge. Switched ignition to Pos-11. No pressure? Started the car and it started immediately and went into high idle again but felt rough like a slight misfire. Fuel pressure registering at 57 psi. As the idle dropped the engine ran lumpy and the fuel pressure fell to 44 psi.

Before I start chasing down a rabbit hole, does anyone actually know what the fuel pressure should be for this car? There seems to be little info on the subject, and what there is is unclear and varies.

One person claims at ignition Pos-II, the car should be at 15 psi. On initial start up it is at 57 psi. That is when there seems to be little info at what it should be at idle. One thread says it is only 45 psi. If this is the case, then other than the initial pressure not registering, the fuel pressure would appear normal. However, compared to a P2 turbo or my 00 V70R that is low at idle.

Switching the engine off, the pressure held for nearly 1.5 hours near 45 psi before slowly dropping which makes me thing the fpr is working ok?

This would suggest to me the issue may not be the fuel system? Thoughts please?

Thanks,

Neil.

[PixelDust]

2008 C-30 manual transmission:

I'm experiencing similar issues, though I've come to this thread not knowing what my fuel pressure is, and having done slight different repairs prior.

My prior work included, head gasket, piston replacement, timing/water pump, VVT Solenoid, oil change, oil pan, plus more.

Im getting a faulty fuel pump signal, though scan tool shows it's being activated.

On top of that I have a bunch of concerning CEM codes with no comms. My testing is pointing toward a bad CEM, but I don't know. Not looking for any answers, cause I don't think anyone has them. Just commiserating.

[scot850]

Check your CEM is not wet and corroded from leaking sunroof drains. There is a join about side window height on the A-pillar and it likes to split with age and leak water onto the CEM above the passenger's toes.

Check the duty cycle of the fuel pump. It should be I believe in the 35% +/- 5 range.

In the end of the day, the issue in this car's case had a multitude of causes. The general random rough running turned out to be a bad aftermarket throttle body the owner had had fitted. Replaced it with a good used Volvo part and all was then good.

Neil.